In many industrial plants, hospitals and other such locations, swinging doors are used in doorways through which both vehicular and foot traffic passes. Oftentimes, the doors in these places are swung to open positions by moving a vehicle, such as a forklift truck, gurney or the like against the door rather than manually pushing the door to an open position. Under these circumstances, the door must be extremely durable and preferably lightweight in construction. The door must be durable so that it will not be damaged to any appreciable extent when subjected to impact forces by vehicles and the like and it must be lightweight in construction so that a minimum force is required to swing the door to an open position.
Conventional industrial doors are made by a number of companies. A typical door of this type is made and sold by RubbAir Door, a division of Eckel Industries, Inc., Cambridge, Massachusetts. The RubbAir door, for instance, has a base provided with processed rubber facings secured thereto so that the door will absorb the shock of impact forces exerted thereon. However, such a door construction requires fastening means between the base material and the rubber facings so as to give rise to possible separation of the facings from the base. This requires maintenance and could even require frequent replacement of the door.
A number of U.S. patents have been directed to panel or door construction for industrial and other types of applications. For instance, U.S. Pat. No. 3,634,971 shows the construction of a refrigerator door using a thermal insulating material within hollow shell. However, the shell is not monolithic in construction. It is made of formed or stamped sheet metal which must be joined at a pair of opposed edges thereof to present the door itself. Moreover, such a door is not adapted to withstand much rough handling and abuse as is required in industrial plants and installations where doors are opened by impact forces exerted by vehicles.
Other publications relating to molded panels or doors include U.S. Pat. Nos. 3,142,095; 3,498,001; and 3,753,843. U.S. Pat. No. 3,142,095 does not teach or suggest a door adapted for heavy-duty industrial applications. Similarly, the other two patents fail to teach a door constructed to meet the demands of such applications. U.S. Pat. No. 3,498,001 shows a two-piece hollow panel that can be separated; and U.S. Pat. No. 3,753,843 shows a panel having a honeycomb core but the panel body is molded onto the core rather than being molded before placement of the core therein, thereby keeping production costs relatively high, yet the panel is not suggested for use as a heavy-duty industrial door.